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In many companies, the methods behind a Scope 3 inventory sit with the sustainability team and the supplier relationships that feed the Category 1 emissions (purchased goods and services) sit with procurement. Under the Greenhouse Gas (GHG) Protocol's current Scope 3 Standard, companies describe the data behind that inventory, but how they disclose it varies widely and is hard to compare from one company to the next.
But the GHG Protocol is now rewriting that standard for the first time since 2011, and a progress update published in March 2026 shows where its technical working group has landed so far. Several of the proposals deal directly with how companies collect and disclose supplier data, and the GHG Protocol's other works in progress, from product-level accounting to the reporting of climate actions, point the same way.
Taken together, the proposals push toward Scope 3 inventories that can be compared across companies, something the GHG Protocol's own guidance says the 2011 standard wasn't designed for. If they go ahead in their current form, it would become far clearer how much of a company's Scope 3 figure comes from its suppliers and how much from estimates.
Where the revision stands
Everything in the progress update is still a working draft, and the GHG Protocol is explicit that its contents could change. In July 2026 it also announced that its Corporate Standard, Scope 2 Guidance, Scope 3 Standard, and work on reporting climate actions will be merged with the International Organization for Standardization's ISO 14064-1 into a single corporate standard, with a joint consultation planned for spring 2027 and publication estimated for late 2028.
Showing what the numbers are made of
The proposal with the widest reach would require companies to break down reported Scope 3 emissions by data type for each category. Two classification options are still on the table. One sorts emissions by whether specific activity data and emission factors were used, with spend-based calculations grouped separately, while the other combines data source and calculation method. Both allow an "Unclassified" option for companies that can't or won't disaggregate.
The GHG Protocol stresses that data type isn't a measure of quality on its own, and the proposal doesn't require any particular kind of data. Its aim is transparency, which in practice means a Category 1 figure built mostly on spend-based estimates would be disclosed as such, alongside peers who have done more of the supplier work.
The Scope 3 Peer Group's 2026 tools review suggests most companies would have a mixed picture to disclose. Of the 144 practitioners surveyed, 18% described their programs as relying on spend or industry-average data, 66% as using a mix of average and supplier-specific primary data, and 15% as predominantly using granular supplier-specific data.
Companies that have some or all of their Scope 3 inventory independently verified would also label it as verified or partially verified, although those that don't verify wouldn't be required to say so.
Fewer shortcuts with diversified suppliers
A second proposal limits how buyers can use the data suppliers already provide. Allocating a share of a supplier's total company emissions, based on spend or volume, would only be allowed for homogeneous suppliers with relatively uniform emissions across their operations, and not for diversified ones.
The working group's reasoning is that a company-wide average spread across very different business units tends to produce unreliable estimates. Where key suppliers make a wide range of products across many sites, buyers would need data at the level of a facility, a production line, or the product itself, a hierarchy the 2011 standard recommends but doesn't enforce. The terms homogeneous and diversified are yet to be defined.
Scope 3 moves into the core inventory
The proposal that raises the stakes most comes from the GHG Protocol's Corporate Standard working group, which wants Scope 3 to be mandatory for any inventory to conform with the Corporate Standard, where today it’s only optional. Combined with the Scope 3 draft, a conforming inventory would need to include Scope 1, Scope 2, and at least 95% of a company's Scope 3 emissions. Companies would quantify everything each year to show exclusions stay under 5%, by rough methods such as hotspot analysis if needed. The 5% threshold matches the boundary the Science Based Targets initiative already requires. Emissions the standard treats as optional, such as some use-phase emissions, would sit outside that floor and be reported separately.
Supplier data as something you report on
The current draft also recommends, without requiring, that companies set goals for the share of their Scope 3 inventory based on specific or primary data and track improvement year on year, partly because many companies don't keep improving data quality after their first reporting effort. One suggested metric is the share of suppliers and other value chain partners that provide specific data.
That looks a lot like the participation figures many companies already track for their supplier engagement programs, now recommended as a measure of Scope 3 data quality.
The development plan for the consolidated standard suggests requirements could go further, listing mandatory primary data and limits on secondary data among the Scope 3 topics under consideration. Neither has reached draft text yet.
Product data and land-based supply chains
One related piece of GHG Protocol work is already settled: the Land Sector and Removals Standard takes effect on January 1, 2027. It applies to companies with significant land-sector activities in their operations or value chain, and it is the first GHG Protocol standard with traceability requirements for Scope 3. For companies buying agricultural ingredients, how much they know about where products are grown will shape what they can report.
The GHG Protocol and ISO are also developing a joint product-level accounting standard, which the GHG Protocol has linked to carbon border measures such as the EU's Carbon Border Adjustment Mechanism (CBAM). Product carbon footprints, the most specific data a supplier can provide, are already appearing in more buyer conversations.
Credit for what suppliers change
The GHG Protocol is developing proposals for reporting climate actions. Companies would keep reporting their emissions inventory as they do now, and report the effect of their climate actions separately, without netting one against the other. Those actions could include buying certificates for low-carbon materials such as steel or cement, or funding projects that cut emissions in their value chain. The approach drew strong support and goes to consultation with the consolidated standard in 2027.
For companies backing projects at supplier sites, such as a move away from fossil-fuel process heat, the GHG Protocol says credible actions that deliver real, verifiable outcomes will be reflected in the future framework. The supplier relationships that produce better data could then also become the way to report what suppliers actually change.
Starting before the final text
Publication isn't expected until the end of 2028, but moving from corporate averages to facility-level data, and from spend-based estimates to supplier-specific ones, depends on supplier relationships that build over several reporting cycles.
Companies that start now would have several years of improving supplier data to point to by the time the final standard is published. Those that wait would make their first disclosures under the new rules with an inventory still largely built on estimates, next to peers already reporting a rising share of supplier-specific data, and a record of improvement can only be built one reporting cycle at a time.
